1. Field of the Invention
The present invention relates to a toner for developing electrostatic images permitting the control of the charge amount of a toner used to develop electrostatic latent images in electrophotography, electrostatic recording, electrostatic printing and others, and charge control resin particles used as a raw material for the production of the same toner.
2. Description of the Prior Art
In copying machines and other equipment based on electrophotography, various dry or wet toners containing a coloring agent, a fixing resin and other substances are used to visualize the electrostatic latent image formed on the photoreceptor having a photosensitive layer containing an inorganic or organic photoconductive substance. The chargeability of such toners is the most important factor in electrostatic latent image developing systems. Thus, to appropriately control the charge amount of toner, a charge control agent providing a positive or negative charge is often added to the toner.
Charge control agents providing a positive charge for toner in actual application include the nigrosine dyes disclosed in Japanese Patent Examined Publication No. SHO41-2427 and elsewhere. Charge control agents providing a negative charge for toner in actual application include the metal complex dyes disclosed in Japanese Patent Examined Publication Nos. SHO41-20153, SHO43-17955, SHO45-26478 and elsewhere. However, most of the charge control agents described above are structurally complex and unstable; for example, they are likely to be decomposed or deteriorated to lose their initial charge control performance when exposed to mechanical friction or impact, temperature or humidity changes, electric impact, light irradiation, etc. Also, many of such conventional charge control agents are colored so that they are unsuitable for use in full-color toners.
As a means for resolving these problems, Japanese Patent Laid-Open No. SHO62-145255, for example, discloses the containment of a metal salt of salicylic acid or a derivative thereof as a charge control agent. Japanese Patent Laid-Open No. SHO63-163374 proposes methods for determining the crystalline structures and crystalline diameters of metal salts of salicylic acid and derivatives thereof to be contained in the toner, with particular mention of zinc 3,5-di-tert-butylsalicylate. Although these substances are advantageous in that they can be used in color toners, their heat stability, uniform dispersibility in resin, or charge control performance, or charging rise speed, in particular, is insufficient so that they remain to be investigated further.
The present invention was developed in view of the aforementioned problems in the prior art and is intended to provide a toner for developing electrostatic images wherein the charge control agent contained therein possesses good heat resistance, good affinity for resin and good dispersibility in resin, which exhibits a high speed of charging rise, which is excellent in charge stability to temperature and humidity changes (environmental resistance) and charge characteristic stability over time (storage stability), and which can be used in various chromatic or achromatic toners, and charge control resin particles used as a starting material for the production of said toner.